Volume rendering is the standard visualization method for viewing two-dimensional (2D) representations of three-dimensional (3D) data sets. A big driving force in the volume rendering field is medical imaging. This is due to the fact that, without the 3D visualization technology, a doctor would is have to estimate the size and the shape of an organ from a plurality of 2D images, obtained by traditional medical scanners, so as to “conceive” the three-dimensional geometrical location of a pathological tissue, which results in difficulty in therapy.
Medical scanners measure three-dimensional space as a structured three-dimensional grid, and this has led researchers to focus mostly on volume rendering techniques based on structured, rectilinear two-dimensional (2D) grids. These grids are often called slices. A 3D volume array of data, which is typically used in volume rendering, is assembled using a series of consecutive slices through a solid body part being scanned. Each grid value of a 2D image array is called a picture element, or “pixel”, while each grid value of a 3D volume array is called a volume element, or “voxel”. The acquisition of a 3D volume array is known in the art and is readily obtainable using systems such as computed tomography (CT) scanning system, helical CT, x-ray, positron emission tomographic (PET), fluoroscopic, confocal microscopic, ultrasound, magnetic resonance (MR) imaging system, etc.
As an example of the advancement in data acquisition methods, OCT (optical coherence tomography) is an optical signal acquisition and processing method allowing extremely high-quality, micrometer-resolution, three-dimensional images from within optical scattering media (e.g., biological tissue) to be obtained. In contrast to other optical methods, OCT, an interferometric technique typically employing near-infrared light, is able to penetrate significantly deeper into the scattering medium, for example ˜3× deeper than its nearest competitor, confocal microscopy. Depending on the use of high-brightness and wide-spectrum light sources such as superluminescent diodes or ultrashort pulse lasers, OCT has achieved sub-micrometer resolution (with very wide-spectrum sources emitting over a ˜100 nm wavelength range). OCT systems, which are commercially available, are finding diverse application in areas such as diagnostic medicine, notably in ophthalmology where it permits remarkable noninvasive images to be obtained from within the retina. In addition, OCT has been actively applied to the field of art conservation and archaeology and has become a new tool for non-invasive examinations of a wide range of museum objects. The more advanced version of OCT technology, spectral-domain optical coherence tomography (SD-OCT), provides even a higher resolution. In the field of ophthalmology, SD-OCT offers a level of detail that parallels—and even enhances the histological observation of retinal integrity.
Improvements in the data acquisition methods, however, are unfortunately not accompanied with improvements in the associated imaging softwares. The SD-OCT units, which are currently available on the market, include 3D OCT-1000 (Topcon), Cirrus HD-OCT (Carl Zeiss Meditec), Spectralis OCT (Heidelberg Engineering), RTVue-100 (OptoVue) and 3D SD-OCT (Bioptigen, Inc). These hardwares are only equipped with imaging softwares which are unable to reconstruct the obtained 2D data into a 3D image in a way that the enhanced capabilities SD-OCT's can be fully taken advantage of. In other words, the subtle changes in the structure and sometimes the function of the scanned object, which are inherent in the scanned data, are easily lost when they are visualized in 3D. This is due to the fact the images these systems create are of low signal-to-noise ratio. Even though these images can be of very high contrast, due to the fact that the slices, which are used to generate these images, can have more or less the same noise distribution, it is difficult for the user to see the topology of the objects (e.g. holes) as one cannot distinguish between the front slice and the slice in the back. The resulted uniform images prevent the medical experts from immediate detection of morphological changes of a tissue of interest.
As a result, there is need for a volume rendering technique that increases the quality of a volume rendered image and maximizes the information, especially the impression of surface topology from the generated image.